Field of the Invention
The invention lies in the semiconductor technology field. More specifically, the present invention relates to a semiconductor component which can be controlled by means of the field effect and which blocks in both directions, as well as to a method for its production.
Semiconductor components which can be controlled by means of the field effect, for example MOSFETs (Metal Oxide Semiconductor Field Effect Transistors), have been known for a long time, for switching currents and for applying voltages to loads. Components of this type have a semiconductor body with first and second doped connecting zones and a channel zone, which is doped in a complementary manner to the first and second connecting zones and is formed between the first and second connecting zones. A control electrode is thereby formed such that it is isolated from the semiconductor body and extends, adjacent to the channel zone, between the first and the second connecting zone. In the case of MOSFETs, the first and second connecting zones form source and drain zones of the component. The channel zone is also referred to as the body region of the component.
A distinction is drawn between MOSFETs of lateral construction and MOSFETs of vertical construction, depending on whether the contact is made with the source and drain zones on one side of the semiconductor body or on opposite sides of the semiconductor body. Stengl and Tihanyi, in xe2x80x9cLeistungs-MOSFET-Praxisxe2x80x9d [Power MOSFET Practice], Pflaum Verlag Munich, 1992, page 36, FIG. 2.2.1B describe a vertical MOSFET, wherein a heavily n-doped drain zone, a p-doped channel zone, and a heavily n-doped source zone are arranged one above the other. Furthermore, a more weakly n-doped drift zone is formed between the heavily n-doped drain zone and the channel zone. Contact is made with the source zone and the drain zone on opposite sides of the semiconductor body, and a number of gate electrodes extend in trenches in the semiconductor body from the source zone through the channel zone into the drift zone, with the gate electrodes being isolated from the semiconductor body by layers of an insulation material. A MOSFET of lateral construction is described in FIG. 2.1 on page 29 of the cited publication, wherein heavily n-doped wells are arranged spaced apart in the semiconductor body and are used as the source zone and drain zone of the component. A gate electrode is arranged on the semiconductor body such that it is isolated by an oxide layer, and extends in the lateral direction from the source zone to the drain zone.
The sequence of the differently doped zones that exist in the described components, namely a source zone and a drain zone of the same conductivity type and a channel zone which is doped in a complementary manner to the source zone and the drain zone, means that there is always a parasitic bipolar transistor in elements such as these, whose base is formed by the channel zone, and whose emitter and collector are formed by the source zone and drain zone, respectively. In order to prevent this parasitic bipolar transistor from affecting the withstand voltage of the component, it is normal for the source zone and channel zone to be short-circuited, as can also be found in the exemplary embodiments of MOSFETs according to the prior art described above.
If the source zone and the channel zone were not short-circuited, charge carriers could accumulate in the channel zone during operation, that is to say when a drive potential is applied to the gate electrode and a forward voltage is applied between the drain zone and the source zone, and these would activate the parasitic bipolar transistor, resulting in a considerable reduction in the withstand or blocking voltage of the MOSFET. The withstand voltage of such a MOSFET in the drain-source direction is only about ⅓ of the withstand voltage of a MOSFET with a short-circuited channel and source zone, wherein the short circuit results in the source zone and the channel zone always being at the same potential, so that no charge carriers can accumulate in the channel zone.
The short-circuiting of the source zone to the channel zone has the disadvantage, however, that the component can now block in only one direction, the drain-source direction, which is normally referred to as the forward direction, while it acts like a diode when a forward voltage is applied in the source-drain direction (reverse direction).
However, in many applications, it is desirable to use a semiconductor component which can be controlled by means of the field effect and can block in both directions when no drive potential is applied. In conventional MOSFETs with a short circuit between the source zone and the channel zone, this can be achieved only by complex additional circuitry measures.
U.S. Pat. No. 5,696,396 (European patent EP 0 656 661 B1) proposes that the short circuit be replaced by a conductive connection with a resistance, in order to increase the voltage drop across the component when a voltage is applied in the rearward direction.
It is accordingly an object of the invention to provide a field-effect controllable semiconductor body and a corresponding fabrication method, which overcome the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and which semiconductor component blocks in both directions and can be produced easily using conventional fabrication means.
With the foregoing and other objects in view there is provided, in accordance with the invention, a field effect-controlled semiconductor component, comprising:
a semiconductor body having a first connecting zone and a second connecting zone of a first conductivity type, and having a channel zone of a second conductivity type formed between the first connecting zone and the second connecting zone;
a control electrode adjacent the channel zone and isolated from the semiconductor body; and
a recombination zone formed in the channel zone and in the second connecting zone and having a recombination material assisting in a recombination of charge carriers of the first and the second conductivity types.
In other words, the novel semiconductor component has a semiconductor body with a first and a second connecting zone of a first conductivity type, and a channel zone of a second conductivity type, which is formed between the first and the second connecting zone. A control electrode is arranged adjacent to the channel zone, such that it is isolated from the semiconductor body. Furthermore, a recombination zone is formed in the channel zone and in the second connecting zone, and has a material which assists the recombination of charge carriers of the first and second conductivity types.
There is no short circuit between one of the two connecting zones and the channel zone in the semiconductor component according to the invention. The semiconductor component according to the invention thus blocks in both directions. The recombination zone in the channel zone prevents activation of a parasitic bipolar transistor which is formed by the sequence of the first connecting zone of the first conductivity type, the second connecting zone of the second conductivity type, and the second connecting zone of the first conductivity type. Specifically, the recombination zone means that charge carriers of the second conductivity type which are injected into the channel zone recombine on the surface of the recombination zone with charge carriers of the first conductivity type, thus preventing accumulation of charge carriers of the second conductivity type in the channel zone.
The recombination zone is preferably composed of a metal, in particular of platinum, or a nitride.
The first connecting zone, the channel zone and the second connecting zone are preferably arranged one above the other in the semiconductor body. In this embodiment, the control electrode is formed in a trench in the semiconductor body, which, starting from one surface of the semiconductor body, extends through the second connecting zone and the channel zone into the first connecting zone.
Furthermore, a drift zone of the first conductivity type, which is more weakly doped than the first connecting zone, can be formed between the first connecting zone and the channel zone, with the control electrode extending only into this drift zone in this embodiment.
One embodiment of the invention provides for the recombination zone to extend in the vertical direction of the semiconductor body, starting from the surface of the semiconductor body, through the second connecting zone into the channel zone. The recombination zone is in this case arranged in a trench which extends into the semiconductor body, wherein case this trench can be completed filled with recombination material, or wherein case only those side surfaces of the trench which face the semiconductor body are covered with recombination material and, apart from this, the trench is filled with a further material, for example an insulation material. The recombination zone can be closed off at the top by one surface of the semiconductor body, or it can end in the trench underneath the surface of the semiconductor body.
The second connecting zone preferably has a first doped region and a second doped region, with the second doped region being doped more strongly than the first doped region and being arranged at a distance from the recombination zone. In this case, a portion of the more weakly doped first region is formed between the second doped region and the recombination zone. The second more strongly doped region is preferably formed adjacent to the insulation layer of the control electrode, and contact is made with it by means of a connecting electrode.
With the above and other objects in view there is also provided, in accordance with the invention, a method of producing a field effect-controllable semiconductor component. The novel method comprises the following method steps:
providing a semiconductor body with a first connecting zone of a first conductivity type, a second connecting zone of the first conductivity type, and a channel zone of a second conductivity type formed between the first and second connecting zones, and wherein the first connecting zone, the channel zone, and the second connecting zone are arranged one above the other;
producing a control electrode that is isolated from the semiconductor body and, starting from a surface of the semiconductor body, extends in a vertical direction into the semiconductor body; and
producing a recombination zone starting from a surface of the semiconductor body and extending through the second connecting zone into the channel zone.
In other words, in the method for producing the semiconductor component, first of all, a semiconductor body with a first connecting zone of a first conductivity type, a second connecting zone of the first conductivity type and a channel zone, which is formed between the first and second connecting zone, of a second conductivity type are provided, with the first connecting zone, the channel zone and the second connecting zone being arranged one above the other in the semiconductor body. A control electrode is then produced, such that it is isolated from the semiconductor body and extends in the vertical direction of the semiconductor body into the semiconductor body. Furthermore, a recombination zone is produced, which extends in the vertical direction of the semiconductor body through the second connecting zone into the channel zone.
The semiconductor body that is provided may also have a drift zone of the first conductivity type, which is doped more weakly than the first connecting zone and is formed between the first connecting zone and the channel zone. If such a drift zone is present, then the control electrode is produced such that it extends from the first connecting zone through the channel zone to the drift zone.
In order to produce the control electrode, a trench is produced in the semiconductor body, with an insulation layer then being applied to exposed regions of the semiconductor body in the trench. After this, an electrode material is introduced into the trench, and this is then covered with an insulation layer.
A trench is likewise produced in the semiconductor body in order to produce the recombination zone. According to one embodiment of the method according to the invention, this trench is filled with a material which assists the recombination of charge carriers of the first and second conductivity types. According to a further embodiment of the method for producing the recombination zone, the invention provides for the trench not to be filled completely with recombination material but only for exposed areas of the semiconductor body in the trench to be covered with recombination material. Apart from this, the trench can then be filled with a different material, for example an insulation material.
In order to isolate the recombination zone in the trench at the top, an insulation layer is preferably applied to the surface of the semiconductor body, covering the trench and regions of the second connecting zone adjacent to the trench. This insulation layer is also used as a mask for a next method step, wherein a heavily doped zone is produced in the second connecting zone, with this heavily doped zone being used as a connection for an electrode.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a semiconductor component which can be controlled by means of the field effect and blocks in both directions, and a method for its production, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.